SAMSUNG S4 Mini switches off randomly

Hardly a year i got my S4 mini via contract at Nashua but the phone is already acting up, it switches off randomly especially while i am on the a call. The sad thing is that i have to charge it every 4 hours. Please Samsung keep up to your brand message check your good and test thoroughly. I should have just stuck to Nokia phones at least they last. Well i will never buy your phones ever!